Non-ferrous metal treatment

ABSTRACT

A method of converting a charge of non-ferrous metal matte in a Pierce-Smith or similar converter. The fluid charge is blown with a total flow of oxidizing gas .Iadd.containing up to about 40% oxygen .Iaddend.effective to maintain autogenous converting temperatures through a plurality of spaced-apart tuyeres limited in number and individual cross-sectional area effective to maintain the gas underexpanded at a pressure within the range from about 50 to about 150 psig so that it penetrates the bath in the form of discrete steady .Iadd.unshielded .Iaddend.jets to positions remote from the tuyere tips thereby reducing degradation of the refractories and build up of accretions. The gas is injected through from three to six tuyeres.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the conversion of non-ferrous metal mattes tothe metal or metal sulphide.

2. Description of the Prior Art

The Pierce-Smith converter has been used widely for this purpose, sincethe turn of the twentieth century, and so converting in this vessel willbe used to exemplify the present invention. The operation of thisapparatus is described in some detail in Extractive Metallurgy of Copperby Newton, Chapter V, Converting; in Extractive Metallurgy of SulfideOres by J. Boldt and P. Queneau, pages 249-252 (1967) and more of thecomplexities of the converting operation may be found in papers such as"Metallurgy of the Converting Process in the Thompson Smelter," a paperprepared for presentation at the 14th Annual Conference ofMetallurgists, Edmonton, Alberta in August 1975, the contents of thesepublications being hereby incorporated by reference.

Fundamentally, the Pierce-Smith converter is made up of a horizontalcylinder providing within it an elongated sealed refractory linedchamber having a cylindrical sidewall and circular endwalls. Thesidewall is provided with a hooded opening for charging and discharginglocated between the endwalls and a row of injection pipes, or tuyeres,entering the chamber through the refractory lining at one side. Thevessel is rotated between a charging position in which the opening isaccessible from the side that it can be charged and a blowing positionin which the charging opening faces upward and is hooded and forms anoff-gas outlet. With the vessel in blowing position air or air slightlyenriched with oxygen is blown in through the tuyeres at low pressure,typically 15 psig to oxidize iron and sulfur in the matte and, thus,effect separation from the matte to form slag and release off-gases,namely, sulfur dioxide. The iron is converted to iron oxide, fluxed withsilica and removed as a slag while the sulfur is oxidized to sulfurdioxide which leaves the converter in the off-gas. Further details ofthe converting operation in the Pierce-Smith converter are contained inthe publications referred to and some of the complexities of chemicalreactions, heat transfer and other relatively complex changes inconditions are described. Through the many years of operation of thistype of converter, a manner of operation has developed which hasundergone little change in the past few years.

There are certain disadvantages that have always plagued the use of thisconverter. For example, the tuyeres become plugged quickly and thusrequire clearing on a regular basis by punching with a metal rod whichis forced through the tuyere. Another problem is that severe refractorywear occurs along the tuyere line, above the tuyeres in the backwall andthe endwalls. This refractory wear is sufficiently excessive that aconverter typically operates for only three months out of four, theother month being required for refractory repair. This results in highmaintenance costs and necessitates excess converter capacity in asmelter operation. A further problem is accretion build-up in theconverter mouth, resulting from the accumulation of particles entrainedin the off-gases and which is a function of the airflow. This build-uprequires frequent cleaning. These problems seem to have been accepted asa fact of life in non-ferrous metal converting using the Pierce-Smithconverter.

Attempts to improve refractory life have been in the area of usingbetter, more wear-resistant refractories as for instance discussed in"The Copper Refractory Symposium" held in New York in 1968. At thatSymposium various factors were described which adversely affectrefractory life and which must be controlled, for example, wide rapidtemperature variations, low-grade matte with resultant large slagvolumes, fine or extremely coarse flux, punching and fluxing practice,low blowing rates, methods of cleaning the converter mouth, andmodifying the normal converter heating periods.

SUMMARY OF THE INVENTION

In the face of the state of the art, the applicants have now found thattuyere plugging and refractory wear are related to the behavior of thegas jets discharging from the tuyere. At pressures at which air isnormally blown into non-ferrous metal converters, that is between 12 and15 psig, the air issues from the tuyere tip in the form of discretebubbles at a frequency of 10 to 12 s⁻¹. The bubbles rise more or lessvertically from the tuyere, break up into smaller bubbles, and washagainst the backwall refractory, while the exothermic oxidationreactions promoted by the injection of the oxidizing gas and resultingfrom the oxidation of sulfur and iron take place in close proximity tothe refractory wall. Moreover, the heat and pumping action of the risingbubbles combine to create rapid wear in the backwall area and also inthe endwalls. The backwall refractory wear is relatively uniform axiallyabove the tuyeres because there is considerable overlap of bubblesforming at adjacent tuyeres. The overlap is caused by the normal closetuyere spacing, for example, 6 to 7 inches, required to achievesufficient air throughput.

Between the formation of successive bubbles at a given tuyere, the bathwashes against the tuyere mouth and promotes the formation of accretionsdue to local freezing and magnetite formation. Successive deposits ofaccretions quickly plug the tuyere, and punching is required. Becausethe accretions attach themselves to the refractories, their abrupt andforced removal by the punching rod leads to pieces of the refractorybreaking off with the accretions. In addition, repeated bubble formationcauses rapid thermal cycling at the tuyere line, which stresses therefractory and accelerates local wear.

The applicants have developed a process which overcomes thesedisadvantages, as will be apparent from the following description. Theconverter, in charging position, is charged to a blowing level withnon-ferrous molten metal matte. The converter is rotated until thetuyeres are submerged, with the .[.control.]. .Iadd.flow.Iaddend.regulated, with sufficient air being introduced to keep thetuyeres open. Then the global air supply is adjusted so that an amountof air is supplied effective to carry out an autogenous convertingreaction at temperatures within the capacity of the converter and atnormal ambient pressure, without overheating, through several tuyereswhose number and individual cross-sectional area is such that the air isunderexpanded and enters the bath horizontally in discrete steady jetsextending some distance downstream from the tuyere tip beforedisintegrating into bubbles. The applicants have found that a preferredinjection pressure is from about 50 to about 150 psig, desirably through4 to 6 tuyeres spaced-apart so as to avoid merging of the jets. Thetuyeres may be in the form of a single group of 3 to 6 tuyeres spacedfrom the endwall and spaced from the mouth of the converter.Alternatively, the tuyeres may be divided into two groups of tuyereswith each group spaced from an endwall and from the mouth of theconverter. Desirably, the tuyeres will have a cross-sectional area fromabout 1 square inch to about 3 square inches and are spaced-apart fromabout 8 inches to about 24 inches. The closest tuyere to the endwallshould be spaced from it at not less than about 36 inches. The spacingof the tuyeres away from the mouth of the converter reduces theturbulence in this area and reduces the accretion formation at the mouthof the converter.

It is thus seen that, according to the invention, air or air enrichedwith oxygen is injected with pressures such that underexpandedconditions are achieved in the tuyere, as compared with the employmentof low pressure gas which issues from the tuyere fully expanded, thatis, with the pressure at the tuyere mouth equal to the local bathpressure. The effect of increasing pressure to create underexpandedconditions is to raise the pressure at the tuyere mouth to a value inexcess of the local bath pressure so that the air discharging from thetuyeres behaves as a steady rather than a pulsating jet and bubbles donot form regularly at the tuyere tip, but instead form some distancedownstream from it. The jet penetrates .[.further.]. .Iadd.farther.Iaddend.into the bath and the tip of the tuyere is continuouslysurrounded by gas. The higer pressures ensure that the jet is pushed.[.further.]. .Iadd.farther .Iaddend.from the backwall because themomentum of the gas from the horizontally positioned tuyeres is greatlyincreased with increasing pressure. The high pressure injection reducesthe problem of backwall refractory erosion by forcing the gas jet.[.further.]. .Iadd.farther .Iaddend.into the bath. The continuouspresence of gas at the tuyere mouth also inhibits the formation ofaccretions. Moreover, accretions that do form are broken off by theaction of the jet. Accordingly, the frequency of tuyere punching isreduced or eliminated altogether as refractory wear at the tuyere lineis reduced.

In the light of normal Pierce-Smith converter practice, one skilled inthe art would expect that the increased pressure at which the air isintroduced would increase splashing and accretion build-up at the mouthof the converter. This may be overcome by limiting the pressure to amaximum of about 150 .[ψ]. .Iadd.psig .Iaddend.and by placing thereduced number of tuyeres away from the converter mouth so that materialejected by the blowing falls back into the bath before reaching themouth. One familiar with conventional blowing practice would also expectthat concentrating the gas in fewer tuyeres would encourage localrefractory wear through higher temperatures being generated in theregion of the tuyere and that the flow of the liquid up the backwallabove the horizontally directed tuyeres would be greater. The applicantshave found, however, that with the steady jet penetrating .[.further.]..Iadd.farther .Iaddend.into the bath away from the backwall, that theextra heat generated is dissipated in the body of the bath and not atthe backwall. One accustomed to the use of a large number of tuyeres atnormal pressures would also expect that injecting the air through fewertuyeres and in the form of jets rather than subdividing it into bubbleswould provide a decrease in oxygen efficiency through lessened interfacebetween the gas and liquid. However, provided their effectivesubmergence within the molten metal is ensured the higher pressure jetshave proven very active and provide good gas-liquid contact. The tips.Iadd.of the tuyeres .Iaddend.should be at a level from about 18 toabout 36 inches beneath the surface of the molten metal.

The applicants' operation in the underexpanded jet regime, by raisingthe pressure to the range from about 50 psig to about 150 psig, shouldnot be confused with operating in the expanded jet regime at smallpressure increases over normal, for example, .Iadd.by .Iaddend.up toabout say 10 to 15 psig as proposed by L. M. Shalygin and V. B.Meyerovich: Tsvet. Metal, 1960, vol. 33, No. 7, pp. 16-19. In order toachieve the results described by the applicants, pressure must be highenough to provide an underexpanded jet regime in which the jet differsin kind from those created at lower pressures while maintaining thetotal amount of oxidizing gas within the range required for themetallurgical operation by reducing the number of jets over thatnormally employed and maintaining their cross-sectional area withinappropriate limits. This requires pressures of at least about 50 .[ψ.]..Iadd.psig. .Iaddend.

Nor should the applicants' procedure be confused with proposals in thenon-ferrous metal field to protect the injectors from the severe resultsof injecting pure oxygen by employing the Joule-Thomson effect createdat high pressures of 400 .[ψ]. .Iadd.psig .Iaddend.or more. Theapplicants' range of pressure is directed merely to changing the jettingconditions from fully expanded to underexpanded, while maintaining thetotal oxidizing gas injected within normal limits of non-ferrousoperations.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the invention, it will be explained morespecifically by reference to the accompanying drawings which should beconsidered as exemplifying preferred embodiments, and in which:

FIG. 1 is a schematic perspective view of a Pierce-Smith converterequipped according to the invention;

FIG. 2 is a schematic diagram of the inside of the converter showing onepreferred arrangement of tuyeres according to the invention set in therefractory; and

FIG. 3 is a schematic diagram showing another arrangement of tuyeresaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring more particularly to the drawings, the Pierce-Smith convertershown is made up of a cylindrical vessel A provided with spaced-apartcircular supporting rings 15 riding on rollers 17 suitably journalled inan infra structure (not shown). A toothed ring 19 adjacent one of therails 15 is engaged by a pinion 21 driven by the shaft 23 by a suitabledrive source so that the vessel A may be rotated about its axis betweena charging position and a blowing position.

The vessel A provides an internal cylindrical chamber having arefractory lined sidewall 25 and refractory lined endwalls 27. Thesidewall 25 is provided with a charging opening 29 surrounds by a skirt31 and provided with a hood 33.

A number of tuyeres B enter the chamber through its sidewall 25 and aresupplied with oxidizing gas from a header 35 which receives its supplyof compressed air or other oxidizing gas from an air inlet pipe 37connected with a suitable source of such gas.

Each tuyere B extends through the .[.iron shell or.]. sidewall 25 .[.andthe refractory lining 26.]. to terminate in a tip .[.24.]. at thesurface of the refractory .[.26.].. The tuyere B may be provided with atuyere puncher.

In accordance with the invention, the number of tuyeres is reducedconsiderably as compared with the number used conventionally. Onepreferred arrangement is shown in FIG. 2. Here there are two groups of 2to 3 tuyeres each spaced from the sidewalls 27 and from the mouth of theconverter. Another preferred arrangement is shown in FIG. 3 where thereis a single group of from 4 to 6 tuyeres spaced from one endwall and toone side of the mouth of the converter.

The tuyeres B may be perpendicular to the sidewall so as to operate inhorizontal blowing position. Alternatively, special effects may beobtained by angling the tuyeres so that the steady jets are injected atan angle of up to about 15° from perpendicular to the refractory wall ofthe vessel. For example, downward injection may increase the efficiencyof the oxidizing gas. Injection at an angle away from the endwall willremove the heating effect of the jet away from the endwall. Injection atan angle away from the mouth of the vessel will reduce turbulence inthat zone and thus reduce accretions.

VARIABLE FACTORS Converters

The Pierce-Smith converter has been described to characterize theinvention, although it may be applied to any non-ferrous furnace usingtuyere side injection of air or of oxygen enriched air.

A typical converter has external dimensions of 13 feet to 15 feet indiameter by 30 feet to 35 feet in length and is made with a 1 inch thickouter iron shell, a 1 to 11/2 inch thick insulating layer of magnesite(MgO), 15 inches of chrome magnesite (MgO--35% Cr₂ O₃) refractorybricks, except the same material is thicker, say about 18 inches, nearthe tuyeres.

Injectors

The injectors or tuyeres, basically the same as in current practice maybe employed, are made from iron and have a straight bore. A typicalinjector has a 11/2 inch to 2 inch inside diameter and is in excess of18 inches to pass through the steel shell, insulating bricks and chromemagnesite bricks and to project some distance outside the vessel. Theinjectors are horizontal when the converter is in blowing position. In aconventional converter there are usually two sets of injectors on eitherside of the mouth with, for example, 40 tuyeres and two sets of 20tuyeres each with spacing approximately 7 inches. All the injectors arethe same. According to the present invention the number of activetuyeres is reduced with a preferred range from 4 to 6 with a spacing ofat least about 15 inches apart.

Each tuyere may blow the same amount of air with several tuyeres linkedto a common manifold. Preferably a separate control is provided for eachtuyere so that the flow rate may be varied along the bath, provided thatthe flow rate is kept within the range stated. The diameters of therespective tuyeres may be varied as may their position in the converter.While the invention has been described and illustrated in connectionwith a furnace equipped with a smaller number of tuyeres than normallyemployed in the prior art, the furnace may be equipped with a largernumber of separately regulatable tuyeres so that a few can be used at atime with the others cut off. This has the advantage that if eventuallythe refractory wear becomes a problem in the region of an active tuyereor set of tuyeres, it or they can be plugged externally and another setactivated. In this way, lining life may be prolonged substantially.

In accordance with the invention the submergence of the tuyeres shouldbe at least about 18 inches.

The tuyere arrangement pattern is to keep the tuyeres away from theendwall to minimize refractory erosion and away from the furnace mouthto minimize splashing problems and accretion build-up at the higher gasinjection rates employed.

Control of the flow through the tuyeres is based on pressure in thetuyeres and/or temperature of the bath. Feedback control using pressuremeasurement may be used to activate tuyere punchers, if found necessary.

Feed Materials

The materials treated are non-ferrous mattes, that is a mixture ofsulphides of copper and iron, and nickel and iron. The commondenominator is the elimination of sulfur as sulfur-dioxide gas, and ironas a siliceous liquid slag of the type fayalite, (FeO)_(x).SiO₂, where1<x<2; this slag also contains variable amounts of Fe₃ O₄. The mattechanges its composition during the cycle, as Fe and S are oxidized, andsubsequently eliminated from the matte. The pressure range of the bathis atmospheric.

One ferrous metal which may be treated according to the invention iscopper matte which usually contains from 20 to 60% copper (as Cu₂ S), 2to 6% oxygen (as iron oxides) with the remainder FeS and minorimpurities. Another is nickel matte with usually from 10 to 50% nickel(Ni₃ S₂) with usually small amount of copper (as Cu₂ S), 2 to 6% oxygen(as iron oxides) with the remainder FeS and minor impurities.

A preferred flux is a siliceous flux containing not less than 80% SiO₂,to improve the heat balance. Flux containing as low as 65% SiO₂ isacceptable.

Oxidizing Gas

The oxidizing gas may be air or air enriched with up to about 40%oxygen. Enrichment with oxygen may be used so as to maintain theautogenous nature of the process and to melt the quantity of coldmaterial that is charged, i.e. to adjust the heat balance. The gas isinjected at a pressure, effective to provide underexpanded conditions.[.with.]. .Iadd.within .Iaddend.the tuyere, from about 50 to about 150.[ψ]. .Iadd.psig .Iaddend.and a linear speed above about 0.9 Mach. Theoverall flow rate is within the range from about 25,000 to 30,000 SCFMfor furnaces of the size mentioned. The oxidizing gas jet is unshieldedand is projected into the fluid charge in the form of a steadyunderexpanded jet as opposed to a pulsing jet. "Underexpanded jet" maybe further explained as follows. When a gas is injected through a tuyereat low pressures, the pressure decreases along the tuyere in thedirection of flow, until at the tip it is equal to the surroundingpressure (atmospheric plus pressure due to bath height). The gas jet isthus fully expanded. As the driving pressure is increased, the gasaccelerates and the pressure drop along the tuyere becomes steeper.However, there is a limit to the velocity that the gas can attain in astraight-bore tuyere, i.e. the speed of sound (Mach 1). Thus at asufficiently high back-pressure the gas reaches a terminal velocity(usually less than Mach 1 owing to frictional effects in the tuyere).Under these conditions the pressure inside the tuyere cannot be releasedby a further acceleration of the gas, and the pressure at the tip isgreater than the ambient pressure. Thus the gas is not fully expanded(underexpanded) relative to the surrounding pressure. The excesspressure is released outside the tuyere by a multidirectional expansionof the gas.

Conditions

The conditions in the furnace during blowing in furnaces of the type andsize exemplified are as follows. The range of temperature .[.of.]..Iadd.at .Iaddend.which converters operate according to the invention isfrom about 1100° C. to about 1300° C. The blowing time is from 6 to 20hours depending on the grade of matte. The input may range from about100 to 200 metric tons of matte depending on the matte grade, with 20 to60 metric tons of flux (again depending on the matte grade). At thisfeed rate the oxygen necessary for the oxidation will be at a rate of4,000 to 8,000 SCFM of oxygen in the oxidizing gas. The output rangesfrom about 70 to about 120 metric tons of copper per cycle and 30 to 80metric tons of slag per cycle. The punching frequency with theconventional process is every 15 to 60 seconds. According to theapplicants' procedure punching is usually not necessary until the end ofthe blow.

Punching will not normally be required during most of the convertercycle. However, the normal punchers are desirably included in theapparatus since they may be required towards the end of the cycle,especially for copper, when the gas flow, and hence temperaturedecreases.

Through the high pressure injection of the invention, the total gas flowrate may be increased up to about 30,000 SCFM in which case thereduction of cycle time will be roughly proportional to the increase inflow rate.

When the furnace is rotated from charging to blowing position, until thedesired submergence is reached, it is desirable to maintain the pressurethrough the tuyeres at from about 10 to about 20 psig with about 15 psigpreferred. Then the pressure may be increased to the desired level.

Th working of the invention will be explained in more detail byreference to the following examples of preferred procedures.

It should be borne in mind that an important factor in determining thelength of a cycle is the grade of the starting material. The grades varyfrom about 20 to about 60% Cu (in the case of copper). This also affectsconverter operation. Therefore, the operation cycle will be describedfor both cases.

High grade mattes are obtained when the concentrates are rich in copperdue to a high content of chalcocite (Cu₂ S) and/or when flash meltingmethods are used to melt the solid concentrates. In such case, it iscommon to obtain a matte with say 55% Cu content. Since a higher contentof Cu implies a lower content of Fe in the matte, smaller amounts ofslag will be produced and the volume of the converter will be occupiedto a larger extent by the value metal, i.e. Cu₂ S (obtained in the firststage of a copper-converting cycle). In such a case, the fresh matte (orstarting matte) will be added fewer times (twice for 55% Cu matte) andthe cycle length will be shorter, since there is less FeS to be oxidizedin the first stage of converting.

EXAMPLE 1

A Pierce-Smith converter was employed 35 feet long by 13 feet indiameter using 6 tuyeres about .[.1/2.]. .Iadd.11/2.Iaddend.inchinternal diameter. The feed material was copper matte (55% Cu). The fluxcontained 85% SiO₂. The oxidizing gas was air.

The following describes a treatment cycle.

First Stage:

1. The converter is hot, having just been emptied .[.from the cycle..]..Iadd.during the previous cycle. .Iaddend.

2. 80 to 100 tons of matte are added through the mouth using ladlesmoved by cranes. 4 to 5 full ladles were needed to charge the converter.The matte was at a temperature of from 1100° to 1150° C.

3. With the converter in loading position (the tuyeres not immersed inthe bath) air is blown through the tuyeres at low pressure, not higherthan 15 .[ψ.]. .Iadd.psig. .Iaddend.

4. The converter is rotated until it reaches blowing position with thetuyeres submerged 18 inches in the molten matte.

5. The blowing pressure is increased to 120 psi .Iadd.psig.Iaddend.immediately after converter reaches blowing position.

6. Air flow is maintained at a rate of about 25,000 SCFM forapproximately 45 minutes. At this point, the converter temperature isapproximately 1200° C. depending on the starting matte temperature.

7. The blowing pressure is decreased to 15 .[.psi,.]. .Iadd.psig,.Iaddend.the converter is rotated to loading position and the air flowturned off.

8. 15 to 20 tons of siliceous flux are added through the convertermouth.

9. Blowing is restarted, following the same steps described in 3, 4 and5 above.

10. After 20 to 30 minutes of blowing, air is shut off according to step7.

11. At this point, the converter temperature is between 1220° to 1240°C. The matte grade would be between 72 to 75% Cu. About 35 tons of slagwill have been produced.

12. Approximately 30 tons of slag (2 ladles) are skimmed off.

13. If the temperature of the converter in step 11 is higher than say1230° C., about 10 tons of cold charge (solid recycle material) areloaded in the converter.

14. 40 to 60 tons of fresh matte (55% Cu) are added to the converter (2to 3 ladles).

15. Some 10 to 20 tons of flux are commonly added at this point.

16. Blowing is started, following steps 3, 4 and 5.

17. Step 6 is repeated.

18. Steps 8 and 9 may or may not be necessary, depending on whether step15 has been performed.

19. After 60 to 80 minutes of blowing (since step 16) the air isshut-off according to step 7.

20. At this point, the converter temperature will be about 1220° C. toabout 1240° C. The matte grade is 78 to 80% (most of FeS, if not all hasbeen oxidized and about 30 tons of slag have been produced) and thisslag is skimmed off into ladles.

21. End of Stage 1; product left in the reactor 80 to 110 tons of Cu₂ S.

Second Stage:

Basically Cu₂ S is the starting raw material. The same FeS and/or fluxmay be present.

22. If the temperature at the end of Stage 1 has been too high (over1240° C. ) and/or if relatively pure copper reverts are available (80%Cu or more) add about 10 tons of cold reverts to the reactor.

23. Blowing is started following steps 3, 4 and 5 of the first stage.

24. The air flow is maintained at about 25,000 SCFM at 120 .[ψ.]..Iadd.psig. .Iaddend.Usually there are no interruptions in the secondstage. The temperature will rise slowly from about 1180° C. to about1220° C. The blowing time will vary depending on the amount of Cu₂ Spresent in the beginning of Stage 2, but it is expected to be 3 to 4hours (overall blowing time for the cycle about 5 to 8 hours. Note: Thisis blowing time. Overall time for the cycle, including charging, waitingfor cranes, etc. will make the cycle 1 to 2 hours longer.

25. When the bath reaches 97 to 98% Cu (an experienced operator can tellthe precise point) pressure is decreased to not more than 15 .[ψ.]..Iadd.psig. .Iaddend.

26. After about 5 minutes the converter is rotated to loading positionand the gas is turned off. Some flux may be added to account for anyiron oxide that may be present.

27. The final product is 60 to 90 tons of blister copper (98.5 to 99.5%Cu).

Low Grade Matte

Low grade mattes are obtained when the concentrates are rich inchalcopyrite and are melted in a reverberatory furnace. In such case itis common to obtain a matte of say 30% Cu content. This means largeramounts of FeS in the matte, a larger volume of slag to be produced andsmaller amounts of Cu (as Cu₂ S) in the reactor.

To overcome this problem, fresh matte is added to the converter severaltimes during the first blowing stage (perhaps 5 times for a 30% Cumatte) and the amounts of flux charged and slag produced changecorrespondingly. However, the converter is operated following the sameprinciple: temperatures not higher than 1250° C. and good estimates ofthe matte grade during the blowing.

EXAMPLE 2

In this case a matte of grade having 30% Cu is treated in a convertersimilar to that of Example 1 using the same flux and air as theoxidizing gas.

The cycle was as follows:

Steps 1, 2, 3 and 4 were the same as in Example 1.

For steps 5 and 6, since the blowing time is longer, the temperature ofthe converter exceeds 1250° C. This is avoided by reducing the blowingpressure to about 80 .[.psi,.]. .Iadd.psig, .Iaddend.through 6 tuyeres,and decreasing the overall flow to not more than 20,000 SCFM.Alternatively, the blowing pressure may be 120 .[.psi,.]. .Iadd.psig,.Iaddend.but employing 4 tuyeres and, again, decreasing the overall flowto not more than 20,000 SCFM.

A further way of avoiding high temperatures is to use 120 .[ψ]..Iadd.psig .Iaddend.blowing pressure, 25,000 SCFM total air injection,and 6 tuyeres, and the addition of larger amounts of cold recycledmaterials. This may be undesirable, due to the more frequentinterruptions in the blowing that would be required. It may also not befeasible, if cold materials are not available in large enough amounts.

Apart from these exceptions, the procedure continues as in Example 1,but the blowing time would be greater (i.e. approx. 60 minutes).

7. The same as in Example 1.

8. 30 tons of flux are required.

9. The same as in Example 1.

10. Blowing time 30 to 45 minutes.

11. The same as in Example 1, except that the matte grade is 45% Cu.

12. 60 tons of slag are produced.

13. Add 10 to 20 tons of cold charge.

14. 60 tons of fresh matte (30% Cu)

15. 30 tons of flux

16. The same as in Example 1.

17. The same as in step 6 for low grade matte as described above.

18. The same as in Example 1.

19. 60 minutes, matte is 55 to 60% Cu.

20. Repeat as from step 12 to step 19 above but change:

12. To about 40 tons of slag.

13. To about 10 tons of cold charge.

14. To about 40 tons of matte.

15. To 20 tons of flux.

16 and 17. The same as in Example 1.

19. 60 minutes, the matte is about 70% Cu.

20 . Repeat steps 12 to 17, but change:

12. 30 tons of slag

13. 10 tons of slag cold revert (may not be necessary).

14. 20 tons of fresh matte

15. 10 tons of flux (otherwise 16 through 21 are the same as in Example1 to end the first stage).

The second stage will be the same as in Example 1.

The following are variables which affect the operation.

The use of .[.enriched.]. oxygen-enriched air improves the heat balanceand shortens the cycle length. It will be useful when,

(a) the matte grade is higher than 50%, and therefore the lower contentof FeS in fresh matte does not allow a large heat generation (coldmattes) in the first stage;

(b) although low grade mattes are available, large amounts of coldmaterials (recycled charge) or even concentrates need to be melted;

(c) during the second stage, specially if a higher flow per tuyere, dueto increased pressures, causes some freezing of the melt in the tuyerezone.

The use of increased gas flow (30,000 SCFM or more) produces a similareffect to an increase in the O₂ concentration, i.e. improves heatgeneration. However, in addition, it may cause excessive amounts ofmaterial from the bath to be carried by the off-gases. It would alsoshorten the cycle length. It would be convenient when,

(a) the tuyeres are located near end of the reactor, and the mouth isnear the other end;

(b) there is a need for larger heat generation as specified above inconnection with the use of oxygen-enriched air;

(c) no fine materials (such as concentrates) are charged into thereactor.

Reference has been made to the first stage of a copper converting cycle.So far Cu can be changed to Ni, bearing in mind that copper is presentas Cu₂ S and nickel as Ni₃ S₂. The operation is basically the same ineach case.

However, once all the iron has been removed as slag, the method toobtain the respective metals differs. In the case of copper, Cu₂ S isoxidized by further blowing of air (or oxygen-enriched air) to obtainCu. But this cannot be done in the case of nickel since that would causeoxidation of Ni to Ni oxides (this can be avoided at highertemperatures, but that is not central to the present invention, since itrequires a different reactor. Therefore, in the case of nickel, thefinal product, according to the present invention, will be Ni₃ S₂(nickel sulfide) that later is converted into Ni by a completelydifferent technique. In the case of copper, the production of the purecopper sulfide, Cu₂ S means the end of the first stage of converting,the second stage being the obtaining of Cu.

We claim:
 1. A method of converting a bath of a nonferrous molten metalmatte .Iadd.and reducing the wear on the refractory and keeping thetuyeres free of blockage .Iaddend.in a converter vessel having anelongated sealed chamber formed by a cylindrical metallic sidewall andcircular endwalls having refractory lining, the sidewall being providedwith a charging port and an off-gas stack, a plurality of metallictuyeres extending into the chamber through the sidewalls torefractory-surrounded exposed tips, means outside the vessel to supplyoxidizing gas under pressure to the tuyeres, and means supporting thevessel on its horizontal axis for rotation between a charging positionand a blowing position in which the tuyere tips are submerged in thebath, the process including a .Iadd.batch .Iaddend.treatment cycle inwhich the vessel is initially charged with molten matte and a pluralityof sequential blows carried out with the vessel being rotated back andforth between said charging and blowing positions and the gas introducedthrough the tuyeres or turned off accordingly for coordinated blowing,charging flux, removal of slag, .Iadd.and .Iaddend.replenishing thecharge, .Iadd.over a time effective to convert the matte to the metal orthe sulfide thereof, .Iaddend.and recovering converted metal from thevessel, comprising,carrying out the blows.Iadd., with the vesselstationary in blowing position, .Iaddend.by injecting into the bath.Iadd.through the tuyeres in steady unshielded streams .Iaddend.a totalflow of .[.oxidizing gas.]. .Iadd.air or air enriched with up to about40% oxygen .Iaddend.effective to maintain autogenous convertingtemperatures within the range from about 1100° C. to about 1300° C.through .[.a plurality of.]. .Iadd.from 3 to 6 submerged .Iaddend.spacedapart tuyeres limited in cross-sectional area and in number .Iadd.at aninjection pressure from about 50 to about 150 psig .Iaddend.effective tocause the gas .Iadd.air .Iaddend.to enter the bath .[.at a pressureeffective to provide discrete underexpanded steady jets.]. .Iadd.inunderexpanded condition from each tuyere as a discrete unshielded jet.Iaddend.which .[.continue.]. .Iadd.continues .Iaddend.to a positionremote from the tuyere .[.tips.]. .Iadd.tip, .Iaddend.whereby wear ofthe refractory lining is reduced substantially to a minimum. .[.
 2. Amethod, as defined in claim 1, in which the oxidizing gas is injectedthrough the tuyeres at a pressure within the range from about 50 toabout 150 psig..]. .[.3. A method, as defined in claim 1, in which gasis injected through from 3 to 6 tuyeres..].
 4. A method, as defined inclaim .[.3.]. .Iadd.1.Iaddend., in which .Iadd.the .Iaddend.tuyeres havean individual cross-section within the range from about 1 square inch toabout 3 square inches.
 5. A method, as defined in claim .[.3.]..Iadd.1.Iaddend., in which the tuyeres are spaced-apart at least about 8inches and spaced from the endwalls at least about 3 feet. .[.6. Amethod, as defined in claim 1, in which the oxidizing gas is injectedthrough from 3 to 6 tuyeres at a pressure within the range from about 50to about 150 psig, each tuyere having a cross-sectional area within therange from about 1 square inch to about 3 square inches, the tuyeresbeing spaced-apart at least about 8 inches and from the endwall at leastabout 3 feet..].
 7. A method, as defined in claim .[.3.]..Iadd.1.Iaddend., wherein the tuyeres are in a single group spaced atleast about 3 feet from one endwall at one side of the middle of theconverter.
 8. A method, as defined in claim .[.3.]. .Iadd.1.Iaddend., inwhich the tuyeres are divided into two groups spaced at respective sidesof the middle of the converter and each spaced at least about 3 feetfrom the end of the converter.
 9. A method, as defined in claim 1, inwhich the vessel is charged in charging position and .[.oxidizing gas.]..Iadd.air .Iaddend.is fed through the tuyeres under expanded conditionswhile the vessel is moved from loading position to blowing position andvice-versa to submerge the tuyeres and the oxidizing gas pressure isthen increased so that the oxidizing gas is underexpanded and blowingcarried out.
 10. A method, as defined in claim 9, in which the.[.oxidizing gas.]. .Iadd.air .Iaddend.is fed through the tuyeres underexpanded conditions at a pressure not greater than about 20 .[ψ]..Iadd.psig .Iaddend.while the vessel is moved from loading position toblowing position and vice-versa to submerge the tuyeres, and a blow isthen carried out by injecting gas through the tuyeres at a pressure fromabout 50 to about 150 .[ψ]. .Iadd.psig. .Iaddend.
 11. A method, asdefined in claim 1, in which the .[.gas.]. .Iadd.air .Iaddend.isinjected at least 15 inches below the surface of the molten charge. 12.A method, as defined in claim 1, in which at least some of the jets aredirected inwardly at an angle from a sidewall.
 13. A method, as definedin claim 1, in which at least some of the jets are directed downwardlyat an angle from the horizontal.
 14. A method, as defined in claim 1,wherein the material treated is copper matte.
 15. A method, as definedin claim 1, in which the material treated is nickel matte.
 16. A method,as defined in claim 1, in which the material treated is copper sulfide..[.17. A method, as defined in claim 1, in which the oxidizing gas isair..]. .[.18. A method, as defined in claim 1, in which the oxidizinggas is air enriched with oxygen up to about 40%..].
 19. A method oftreating a bath of a non-ferrous molten metal matte .Iadd.and reducingthe wear on the refractory and keeping the tuyeres free of blockage.Iaddend.in a converter vessel having an elongated sealed chamber formedby cylindrical metallic .[.sidewall.]. .Iadd.sidewalls .Iaddend.andcircular endwalls, the .[.sidewall.]. .Iadd.sidewalls .Iaddend.beingprovided with a charging port and an off-gas stack, a plurality ofmetallic tuyeres extending into the chamber through the sidewalls torefractory-surrounded exposed tips, means outside the vessel to supply.[.oxidizing gas.]. .Iadd.air or air enriched with up to about 40%oxygen .Iaddend.under pressure to the tuyeres, and means supporting thevessel on its horizontal axis for rotation between a charging positionand a .Iadd.stationary .Iaddend.blowing position in which the tuyeretips are submerged in the bath, the process including a treatment cyclein which the vessel is initially charged with molten matte and aplurality of sequential blows carried out with the vessel being rotatedback and forth between said charging and blowing positions and the.[.gas.]. .Iadd.air .Iaddend.introduced through the tuyeres or turnedoff accordingly for coordinated blowing, charging flux, removal of slag,.Iadd.and .Iaddend.replenishing the charge .Iadd.over a time effectiveto convert the matte to the metal or the sulfide thereof.Iaddend., andrecovering converted metal from the vessel, comprising,initiallycharging the vessel in loading position with molten matte, rotating thevessel into blowing position with the tuyeres submerged to at leastabout 18 inches while injecting .[.gas.]..Iadd.the air .Iaddend.throughthe tuyeres at a pressure at which the gas is expanded, then carryingout a cycle of blows.Iadd., with the vessel in stationary blowingposition, .Iaddend.by injecting .Iadd.into the bath through tuyeres inunshielded streams .Iaddend.a total flow of .[.oxidizing gas.]..Iadd.air or air containing up to about 40% oxygen .Iaddend.effective tomaintain autogenous converting conditions at temperatures within therange from about 1100° C. to about 1300° C. through from 3 to 6 tuyereshaving an individual cross-section within the range from about 1 squareinch to about 3 square inches spaced-apart from about 8 to 24 inches andspaced from the endwalls at least about 3 feet at a pressure within therange from about 50 to about 150 psig effective to cause the gas.Iadd.air streams .Iaddend.to enter the bath at a pressure effective toprovide discrete .Iadd.unshielded .Iaddend.underexpanded steady jetswhich continue to a position remote from the tuyere tips whereby wear ofthe refractory lining is reduced substantially to a minimum, the jetsentering the bath at least 18 inches below the surface of the moltencharge.
 20. A method, as defined in claim 1 or 19, in which the totalblowing time is at least .[.60 .]. .Iadd.6 .Iaddend.hours.
 21. A method,as defined in claim 19, in which the .[.oxidizing gas.]. .Iadd.air.Iaddend.is fed through the tuyeres under expanded conditions at apressure not greater than about 20 .[ψ]. .Iadd.psig .Iaddend.while thevessel is moved from loading position to blowing positon and vica-versato submerge the tuyeres, and a blow is then carried out by injecting.[.gas.]. .Iadd.the air .Iaddend.through the tuyeres at a pressure fromabout 50 to about 150 .[ψ]. .Iadd.psig.Iaddend..
 22. A method, asdefined in claim 19, wherein the material treated is copper matte.
 23. Amethod, as defined in claim 19, in which the material treated is nickelmatte.
 24. A method, as defined in claim 19, in which the materialtreated is copper sulfide. .[.25. A method, as defined in claim 19, inwhich the oxidizing gas is air..]. .[.26. A method, as defined in claim19, in which the oxidizing gas is air enriched with oxygen up to about40%..].